Receiving device

ABSTRACT

A receiving device that receives a signal in a receiving antenna. The receiving device includes a gain controller that adjusts a gain in the receiving device in response to information related to power of the signal, and a signal detector that determines whether, within a predetermined period after the information related to the power of the signal exceeds a first threshold value, the information related to the power of the signal exceeds a second threshold value which is larger than the first threshold value. The gain controller adjusts a search range of the gain in the receiving device based on a determination result of the signal detector with respect to the information related to the power of the signal.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2014-020660, filed on Feb. 5, 2014, the contents of which are herebyincorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a receiving device that controls again in response to power of a received signal.

2. Description of the Related Art

For wireless local area networks (LANs), the standardization of, forexample, the Institute of Electrical and Electronics Engineering, Inc.(IEEE) 802.11ad communication specifications has been promoted. In IEEE802.11ad, an access control method referred to as carrier sense multipleaccess/collision avoidance (CSMA/CA) has been adopted.

In CSMA/CA, a receiving device detects a signal existing in a wirelesstransmission path, and adjusts a gain for amplifying the detected signalsuch that a fluctuation range of the detected signal falls within adynamic range of an analog-digital converter (ADC). In IEEE 802.11ad, atraining sequence referred to as a preamble is given to the head of apacket, and the receiving device performs automatic gain control (AGC)using the preamble.

As a technique by which AGC converges at a high speed in a limitedpreamble section, a technique in, for example, Japanese UnexaminedPatent Application Publication No. 2005-278017 is known. A wirelesscommunication device described in Japanese Unexamined Patent ApplicationPublication No. 2005-278017 stores an optimum gain value for AGC in pastcommunication, and sets the stored gain value as a standby gain valuefor each AGC circuit during a standby period, thereby reducing theconvergence time before an optimum gain value is decided whencommunication is resumed.

SUMMARY

In Japanese Unexamined Patent Application Publication No. 2005-278017,when the wireless communication device communicates with a terminallocated close to the wireless communication device (referred to as a“terminal A” for convenience) and a terminal located distant from thewireless communication device (referred to as a “terminal B” forconvenience), a gain value for AGC in the communication with theterminal A converges on a small gain value because the distance isshort.

However, when the gain value for AGC that has converged in thecommunication with the terminal A is set as a standby gain value, thestandby gain in the wireless communication device is small. Therefore,there is a problem in that it takes time for AGC to converge for asignal arriving from the distant terminal B, signal demodulation isdelayed, and the signal detection accuracy is degraded. In addition,when the terminal A is moved, the standby gain in the wirelesscommunication device becomes unsuitable. Therefore, there is also aproblem in that it takes time for AGC to converge, signal demodulationis delayed, and the signal detection accuracy is degraded.

One non-limiting and exemplary embodiment provides a receiving devicethat enhances the speed of convergence of AGC processing and suppressesdegradation of the detection accuracy for a received signal, regardlessof whether a device with which the receiving device communicates ischanged or moved.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and Figures. The benefits and/oradvantages may be individually provided by the various embodiments andfeatures of the specification and drawings disclosure, and need not allbe provided in order to obtain one or more of the same.

In one general aspect, the techniques disclosed here feature a receivingdevice that receives a signal in a receiving antenna. The receivingdevice includes a gain controller that adjusts a gain in the receivingdevice in response to information related to power of the signal, and asignal detector that determines whether, within a predetermined periodafter the information related to the power of the signal exceeds a firstthreshold value, the information related to the power of the signalexceeds a second threshold value which is larger than the firstthreshold value. The gain controller adjusts a search range of the gainin the receiving device based on a determination result of the signaldetector with respect to the information related to the power of thesignal.

A receiving device according to the present disclosure can enhance thespeed of convergence of AGC processing and suppress degradation of thedetection accuracy for a received signal, regardless of whether a devicewith which the receiving device communicates is changed or moved.

These general and specific aspects may be implemented using a system, amethod, and a computer program, and any combination of systems, methods,and computer programs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically illustrating an internalconfiguration of a receiving device of a present embodiment;

FIG. 2 is a block diagram illustrating in detail the internalconfiguration of the receiving device of the present embodiment;

FIG. 3 schematically illustrates a structure of a packet received by thereceiving device of the present embodiment and a structure of a preambleadded to the head of the packet;

FIG. 4A illustrates correlation detection, and FIG. 4B illustrates powerdetection;

FIG. 5 is a block diagram illustrating in detail an example of aninternal configuration of a power detection unit of the presentembodiment;

FIG. 6A illustrates power detection timings when signal receptionintensities are weak, medium, and strong, and FIG. 6B illustrates outputtimings of a first determination signal and a second determinationsignal when signal reception intensities are weak, medium, and strong;

FIG. 7 illustrates a first determination signal, a gate signal, and asecond determination signal when signal reception intensities are strongand medium;

FIG. 8 is a flowchart illustrating an example of an operating procedurefor power detection in the power detection unit of the receiving deviceof the present embodiment;

FIG. 9 is a flowchart illustrating an example of an operating procedurefor gain search range setting in a gain search range setting unit of thereceiving device of the present embodiment;

FIG. 10A is a block diagram illustrating in detail an internalconfiguration of a power detection unit of a first variation, and FIG.10B illustrates an example of a relationship of counting unit outputswhen signal reception intensities are strong and medium;

FIG. 11 is a block diagram illustrating in detail an internalconfiguration of a power detection unit of a second variation; and

FIG. 12A is a block diagram illustrating in detail an internalconfiguration of a power detection unit of a third variation, and FIG.12B illustrates an example of a relationship of integration unit outputswhen signal reception intensities are strong and medium.

DETAILED DESCRIPTION

An embodiment of a receiving device according to the present disclosure(referred to below as the “present embodiment”) will now be describedwith reference to the drawings. The receiving device of the presentembodiment is an information communication terminal that complies withwireless LAN communication specifications (for example, IEEE 802.11ad),and is, for example, a smartphone or tablet terminal. However, thereceiving device of the present embodiment is not limited to asmartphone or tablet terminal.

FIG. 1 is a block diagram schematically illustrating an internalconfiguration of a receiving device 100 of the present embodiment. FIG.2 is a block diagram illustrating in detail the internal configurationof the receiving device 100 of the present embodiment. The receivingdevice 100 illustrated in FIG. 1 includes a radio-frequency signalprocessing circuit RFC to which a receiving antenna Ant is connected, ananalog-digital conversion unit 104, a signal detection unit DTS, a gaincontrol unit GCNT, a demodulation unit 113, and a decoding unit 114.

The radio-frequency signal processing circuit RFC includes a low noiseamplifier (LNA) 101, a mixer (MIX) 102, and a variable gain amplifier(VGA) 103. The signal detection unit DTS includes a correlationcomputation unit 105, a correlation detection unit 106, a powercomputation unit 107, a power detection unit 108, and a packet detectionunit 109. The gain control unit GCNT includes a standby gain settingunit 110, a gain search range setting unit 111, and a gain decision unit112. That is, the receiving device 100 uses the signal detection unitDTS to determine a state of a received signal using information relatedto power of the input signal, and uses the gain control unit GCNT todecide a gain search range based on the determined state of the receivedsignal. Information related to power of a signal may be an absolutevalue of an amplitude of the signal, the power, the number of times thepredetermined power has occurred, or an integration value of the power.

The operation of the units of the receiving device 100 illustrated inFIG. 1 or FIG. 2 will now be described.

The receiving antenna Ant receives a radio-frequency signal (forexample, a millimeter-wave) transmitted from the outside, which is adevice with which the receiving device 100 communicates (for example, atransmitting device, not illustrated). The radio-frequency signalreceived in the receiving antenna Ant is input to the radio-frequencysignal processing circuit RFC.

The radio-frequency signal processing circuit RFC amplifies theradio-frequency signal received in the receiving antenna Ant using again decided by the gain control unit GCNT. The radio-frequency signalprocessing circuit RFC converts the radio-frequency signal received inthe receiving antenna Ant to a baseband signal using a local oscillationsignal in the receiving device 100 (local signal, not illustrated). Thebaseband signal is input to the analog-digital conversion unit 104.

The low noise amplifier 101 amplifies the radio-frequency signalreceived in the receiving antenna Ant using a gain for the low noiseamplifier 101 decided by the gain decision unit 112, and outputs thesignal to the mixer 102.

The mixer 102 down-converts the frequency of the radio-frequency signalamplified by the low noise amplifier 101 and converts theradio-frequency signal to a baseband signal using a local oscillationsignal in the receiving device 100 (local signal, not illustrated), andoutputs the signal to the variable gain amplifier 103.

The variable gain amplifier 103 amplifies the baseband signal outputfrom the mixer 102 using a gain for the variable gain amplifier 103decided by the gain decision unit 112, and outputs the signal to theanalog-digital conversion unit 104.

The analog-digital conversion unit 104 samples and quantizes the analogbaseband signal amplified by the variable gain amplifier 103 to performanalog-digital (AD) conversion to a digital baseband signal, and outputsthe signal to the correlation computation unit 105, the powercomputation unit 107, and the demodulation unit 113.

After the standby gain setting unit 110, which will be described later,sets a standby gain, the receiving device 100 enters a received signalstandby status. When the receiving device 100 stands by for a signal,the product (the sum in decibels) of a gain for the low noise amplifier101 and a gain for the variable gain amplifier 103 is defined as a“standby gain”.

In a received signal standby status, the signal detection unit DTSdetermines whether a signal is detected, based on a power computationvalue and a cross-correlation value (see the later description) of thesignal quantized by the analog-digital conversion unit 104 (referred tobelow as a “quantized signal”). When it is determined that a signal isdetected, the signal detection unit DTS outputs a carrier sense signalthat provides notification of the signal detection.

As described below, the correlation computation unit 105 performscorrelation computation of a quantized signal and a known sequenceretained in advance (see the later description) to calculate across-correlation value. The correlation detection unit 106 detects thesignal using the cross-correlation value. In the present disclosure, asignal detection method by which whether there is a signal is determinedusing the correlation computation unit 105 and the correlation detectionunit 106 is defined as “correlation detection”.

Moreover, the power computation unit 107 outputs a power computationvalue of a signal. The power detection unit 108 detects the signal usingthe power computation value. In the present disclosure, a signaldetection method by which whether there is a signal is determined usingthe power computation unit 107 and the power detection unit 108 isdefined as “power detection”.

Specifically, the packet detection unit 109 uses a cross-correlationvalue computed by the correlation computation unit 105 as a firstcriterion for determining signal detection, and uses a signal powercomputation value computed by the power computation unit 107 as a secondcriterion for determining signal detection. The packet detection unit109 determines whether a signal (packet) is detected, using a powerdetection result based on the signal power computation value and acorrelation detection result based on the cross-correlation value.

That is, the packet detection unit 109 estimates that a signal receptionintensity is strong or not strong in accordance with the signaldetection methods listed in Table 1 (that is, whether a signal isdetected through power detection or through correlation detection), andoutputs a reception intensity estimation result to the gain search rangesetting unit 111. Table 1 lists a correspondence relationship betweenthe signal detection methods and signal reception intensities.

TABLE 1 Signal detection method Signal reception intensity Powerdetection Strong Correlation detection Not strong (= medium or weak)

When it is determined that a signal is detected, the packet detectionunit 109 outputs a carrier sense signal that provides notification ofthe signal detection. In addition, when it is determined that thedetected signal is a signal from a local system (see the laterdescription), the packet detection unit 109 outputs a control signal fordemodulating the detected signal to the demodulation unit 113.

The correlation computation unit 105 computes a cross-correlation valueof a quantized signal and a known sequence retained in advance by thecorrelation computation unit 105, and outputs the cross-correlationvalue to the correlation detection unit 106. The known sequence is, forexample in IEEE 802.11ad, a Golay sequence that constitutes a preamblePRB added to the head of a packet as illustrated in FIG. 3, but notlimited to a Golay sequence. FIG. 3 schematically illustrates astructure of the packet received by the receiving device 100 of thepresent embodiment and a structure of the preamble PRB added to the headof the packet.

A transmitting device (not illustrated), which is a device with whichthe receiving device 100 communicates, transmits a packet with thepreamble PRB added to the head. The preamble PRB is configured tocombine a plurality of known sequences A1, A2 to AN. Each of the Nsequences A1, A2 to AN may be identical or may have a reversed sign.Each of A1, A2 to AN can be represented as A or −A using a single knownsequence A.

That is, the correlation computation unit 105 retains the known sequenceA that becomes a basis for a plurality of known sequences A1 to AN, andcomputes a cross-correlation value of the plurality of known sequencesA1 to AN in the preamble PRB added to the head of a quantized signal(received signal) and the known sequence A retained in advance (see FIG.4A). FIG. 4A illustrates correlation detection.

The correlation detection unit 106 makes a comparison between thecross-correlation value computed by the correlation computation unit 105and a predetermined correlation threshold value illustrated in FIG. 4A,and determines whether a peak value of the cross-correlation valuecomputed by the correlation computation unit 105 exceeds the correlationthreshold value illustrated in FIG. 4A. The correlation detection unit106 outputs, to the packet detection unit 109, a result of determiningwhether the peak value of the cross-correlation value computed by thecorrelation computation unit 105 exceeds the correlation threshold valueillustrated in FIG. 4A.

By appropriately adjusting the correlation threshold value, the peakvalue of the cross-correlation value computed by the correlationcomputation unit 105 exceeds the correlation threshold value illustratedin FIG. 4A, when a signal from a local system (see the laterdescription) is received by the receiving device 100. However, the peakvalue of the cross-correlation value does not exceed the correlationthreshold value illustrated in FIG. 4A, when an interference signal fromanother system is received by the receiving device 100.

Accordingly, the packet detection unit 109 can determine whether aquantized signal is a received signal from a local system or aninterference signal from another system through correlation detection inthe correlation computation unit 105 and the correlation detection unit106.

Further, the correlation computation unit 105 can improve an SNR of apeak value of a cross-correlation value by using, as a known sequence,one with high characteristics for suppressing cross-correlation valueside lobe. For example, a Golay sequence used in IEEE 802.11ad has highcharacteristics for suppressing cross-correlation value side lobe.

With a sequence that can ideally suppress side lobe, an SNR of a peakvalue of a cross-correlation value is multiplied by a sequence length ofan SNR of a quantized signal (received signal). For example, when asequence length is 128 symbols, an SNR is multiplied by 128. Even thoughan SNR of a quantized signal (received signal) is small, that is, thereception intensity of the signal received by the receiving device 100is weak, an SNR of a peak value of a cross-correlation value is large,and therefore the detection accuracy using the cross-correlation valueis high.

On the other hand, until at least the entire known sequence A1 isreceived by the receiving device 100, a peak value of thecross-correlation value computed by the correlation computation unit 105does not occur. In FIG. 4A, for example, when a sequence length of aknown sequence is 128 symbols, a peak value of a cross-correlation valueoccurs 128 symbols after the start of reception of a quantized signal.That is, waiting time is required for a determination of signaldetection using correlation detection.

After a standby gain is set, the power computation unit 107 squares, forexample, an amplitude of a signal to average samples in a certain periodof time (for example, 16 samples), and thereby computes the power of thesignal and then outputs the power value to the power detection unit 108,the standby gain setting unit 110, and the gain decision unit 112. FIG.4B illustrates power detection.

In the present embodiment, the packet detection unit 109 determines thatthe signal is detected, based on a power detection result from the powerdetection unit 108 with respect to the signal power value computed bythe power computation unit 107. Moreover, the packet detection unit 109may determine that the signal is detected when the signal power valuecomputed by the power computation unit 107 exceeds a predetermined powerthreshold value (see FIG. 4B).

The packet detection unit 109 can detect a signal transmitted from alocal system (for example, a transmitting device that complies with thesame communication specifications (IEEE 802.11ad) as those in thereceiving device 100; the same applies below), through power detectionusing a signal power value, and can also detect an interference signaltransmitted from another system (for example, a transmitting device thatcomplies with different communication specifications from those in thereceiving device 100; the same applies below).

In FIG. 4B, at the timing at which the receiving device 100 receives asignal, a total power value of the signal and thermal noise rises in arelatively short amount of time with respect to a time length of thereceived signal. Therefore, the instantaneousness of signal detection ishigh, that is, the time required for signal detection is short. Forexample, when a power value of a signal is sufficiently large withrespect to a power value of thermal noise, and a receptionsignal-to-noise ratio (SNR), which indicates the strength of a receptionintensity of a signal received from a device with which the receivingdevice 100 communicates, is high, a total power value of the signal andthermal noise rises quickly. However, as the SNR becomes lower, a signaldetection timing becomes slower because a signal power value isdistorted due to external noise and rises slowly.

The power detection unit 108 determines whether the reception intensityof the signal received from a transmitting device, which is a devicewith which the receiving device 100 communicates, is strong, based onthe signal power value computed by the power computation unit 107. Then,the power detection unit 108 outputs a result of determining whether thesignal reception intensity is strong (referred to below as a “powerdetection result”) to the packet detection unit 109. The detailedoperation of the power detection unit 108 will be described later withreference to FIGS. 5 to 8.

In a received signal standby status, the gain control unit GCNT monitorsthe power of the thermal noise quantized by the analog-digitalconversion unit 104. The gain control unit GCNT adjusts a gain searchrange for AGC processing appropriate to the power value of the receivedsignal detected by the packet detection unit 109, using a receptionintensity estimation result (see the later description) output from thepacket detection unit 109.

After the packet detection unit 109 determines that the signal isdetected, the gain control unit GCNT controls each of gains for the lownoise amplifier 101 and the variable gain amplifier 103 such that afluctuation range of the level of the detected signal falls within adynamic range of the analog-digital conversion unit 104.

In a received signal standby status, the standby gain setting unit 110monitors the power value of the thermal noise quantized by theanalog-digital conversion unit 104. The standby gain setting unit 110decides each of gains for the low noise amplifier 101 and the variablegain amplifier 103 such that the power value of the quantized thermalnoise is equal to a predetermined standby power target value.

The standby power target value is, for example, a predeterminedpercentage of a power value for maximizing an output amplitude of theanalog-digital conversion unit 104 (for example, 30%). The product (thesum in decibels) of a gain for the low noise amplifier 101 and a gainfor the variable gain amplifier 103 in a standby status is referred tobelow as a “standby gain Gs”.

The standby gain setting unit 110 adjusts the standby gain to be a largevalue such that the power value of the thermal noise quantized by theanalog-digital conversion unit 104 is equal to the standby power targetvalue. Accordingly, even though the power value of the signal quantizedby the analog-digital conversion unit 104 is small, the receiving device100 can adjust the power value of the signal amplified by the low noiseamplifier 101 and the variable gain amplifier 103 so that the powervalue of the signal is equal to or larger than the quantizationresolution of the analog-digital conversion unit 104.

In accordance with Table 2, the gain search range setting unit 111adjusts and sets a gain search range for AGC processing appropriate tothe power value of the received signal detected by the packet detectionunit 109, using a reception intensity estimation result output from thepacket detection unit 109. The gain search range for AGC processing is again search range for each of gains for the low noise amplifier 101 andthe variable gain amplifier 103. Table 2 lists an example of arelationship between the signal reception intensities and gain searchranges. The specific operation of the gain search range setting unit 111of the gain control unit GCNT will be described later with reference toFIG. 9.

TABLE 2 Signal reception intensity Gain search range Strong Widened Notstrong Narrowed

In the gain search range set by the gain search range setting unit 111,the gain decision unit 112 performs AGC processing using the standbygain set by the standby gain setting unit 110 and the received signalpower value computed by the power computation unit 107.

That is, in the gain search range set by the gain search range settingunit 111, the gain decision unit 112 decides each of gains for the lownoise amplifier 101 and the variable gain amplifier 103 such that thepower value of the received signal detected by the packet detection unit109 is equal to a predetermined reception power target value. Theproduct (the sum in decibels) of a gain for the low noise amplifier 101and a gain for the variable gain amplifier 103 is referred to below as a“total gain”.

After deciding each of the gains for the low noise amplifier 101 and thevariable gain amplifier 103, the gain decision unit 112 sets the gainfor the low noise amplifier 101 in the low noise amplifier 101 and alsosets the gain for the variable gain amplifier 103 in the variable gainamplifier 103. The reception power target value is, for example, apredetermined percentage of a power value for maximizing an outputamplitude of the analog-digital conversion unit 104 (for example, 60%).The reception power target value is higher than the standby power targetvalue.

When the power value of the received signal quantized by theanalog-digital conversion unit 104 is smaller than the reception powertarget value, the gain decision unit 112 makes the total gain larger.When the power value of the received signal is larger than the receptionpower target value, the gain decision unit 112 makes the total gainsmaller. When the power value of the received signal does not reach thereception power target value within the prescribed time for AGCprocessing, it is assumed that a timeout has occurred in the AGCprocessing, and the gain decision unit 112 forces termination of the AGCprocessing.

The demodulation unit 113 starts demodulation of the received signalquantized by the analog-digital conversion unit 104 in response to acontrol signal output from the packet detection unit 109, and outputs ademodulation result to the decoding unit 114. After the AGC processingin the signal detection unit DTS and the gain control unit GCNTconverges, the demodulation unit 113 demodulates a header HED region anda payload PLD region illustrated in FIG. 3 in this order.

The decoding unit 114 performs predetermined error correction decodingprocessing for the demodulation result from the demodulation unit 113,reconstructs information bits transmitted from the transmitting device,and outputs the information bits to the subsequent stage. In the packettransmitted from the transmitting device, predetermined error correctioncodes are added to the header HED and the payload PLD. The header HED isa field that stores control information required for demodulation of thepayload PLD. The payload PLD is information data other than the controlinformation stored in the preamble PRB and the header HED, and is, forexample, image data.

(Detailed Configuration and Operation of the Power Detection Unit 108 ofthe Receiving Device 100)

The detailed configuration and operation of the power detection unit 108of the receiving device 100 of the present embodiment will next bedescribed with reference to FIGS. 5 to 8. FIG. 5 is a block diagramillustrating in detail an example of an internal configuration of thepower detection unit 108 of the present embodiment. FIG. 6A illustratespower detection timings when signal reception intensities are weak,medium, and strong. FIG. 6B illustrates output timings of a firstdetermination signal and a second determination signal when signalreception intensities are weak, medium, and strong. FIG. 7 illustrates afirst determination signal, a gate signal, and a second determinationsignal when signal reception intensities are strong and medium.

In FIG. 6A, for (a) which indicates a power value when a signalreception intensity is weak, the power value does not exceed apredetermined power threshold value, and therefore signal detectionthrough power detection is not determined. However, because signaldetection through correlation detection is determined, reception ispossible.

For (c) which indicates a power value when a signal reception intensityis strong, the power value exceeds the predetermined power thresholdvalue after the computation of the power value by the power computationunit 107 (time point ta), and therefore a gain search range is setwidely. However, because the time required before signal detection isshort (time point ta), reception is possible even though the convergencetime of AGC processing is long. The time point ta is a timing of signaldetection through power detection when a signal reception intensity isstrong.

However, for (b) which indicates a power value when a signal receptionintensity is medium, the power value transitions near the predeterminedpower threshold value due to, for example, an influence of externalnoise, and has uncertainty about whether or not the power value exceedsthe power threshold value, thereby causing the time required beforesignal detection to be long (time point tb). The time point tb is atiming of signal detection through power detection when a signalreception intensity is medium. Therefore, when a signal receptionintensity is medium, the time required for power detection may be long,and may be nearly equal to the time required for correlation detection.

Accordingly, for (b) which indicates a power value when a signalreception intensity is medium, it is determined that a signal isdetected through power detection at the time point tb, and a wide gainsearch range is set. Therefore, the convergence time of the AGCprocessing in the gain decision unit 112 is long. When both the timerequired before power detection and the time required before convergenceof AGC processing are long, the start of demodulation in thedemodulation unit 113 is delayed and there is a higher probability thatan error occurs in the information bits reconstructed by the decodingunit 114.

In the present embodiment, the signal detection unit DTS uses a methodby which when an SNR of a received signal, that is, the receptionintensity of the signal transmitted from a device with which thereceiving device 100 communicates is medium, the signal is detectedthrough correlation detection, and further, when the SNR (signalreception intensity) of the received signal is strong, power detectionis performed.

Therefore, when the reception intensity of the signal transmitted fromthe device with which the receiving device 100 communicates is medium,the signal detection unit DTS detects the signal through correlationdetection and the gain search range setting unit 111 narrows a gainsearch range for AGC processing. Accordingly, the time required beforeconvergence of the AGC processing in the gain decision unit 112 isshort, and therefore the receiving device 100 can suppress a delay inthe start of demodulation in the demodulation unit 113 and suppressoccurrence of a reception error.

The specific configuration and operation of the power detection unit 108illustrated in FIG. 5 will next be described. The power detection unit108 illustrated in FIG. 5 has a power value first determination unit201, a power value second determination unit 202, a gate signalgeneration unit 203, and a gate unit 204.

The power value first determination unit 201 makes a comparison betweenthe power value of the signal computed by the power computation unit 107(referred to below as a “computed power value”) and a predeterminedfirst power threshold value. When the computed power value of the signalexceeds the first power threshold value, the power value firstdetermination unit 201 outputs a first determination signal to the gatesignal generation unit 203. The first power threshold value is apredetermined percentage of a signal power value for maximizing anoutput amplitude of the analog-digital conversion unit 104, and thispercentage exceeds the standby power target value (for example, 50%).

The power value second determination unit 202 makes a comparison betweenthe computed power value of the signal computed by the power computationunit 107 and a predetermined second power threshold value. When thecomputed power value of the signal exceeds the second power thresholdvalue, the power value second determination unit 202 outputs a seconddetermination signal to the gate signal generation unit 203. The secondpower threshold value is a predetermined percentage of a signal powervalue for maximizing an output amplitude of the analog-digitalconversion unit 104, and this percentage exceeds the standby powertarget value (for example, 70%).

The gate signal generation unit 203 generates a gate signal for apredetermined gate period after the input of the first determinationsignal (for example, from a time point tgs to a time point tgeillustrated in FIG. 7). The predetermined gate period is set to beshorter than a delay time allowed for power detection such that thestart of signal demodulation in the demodulation unit 113 is notdelayed.

For example, when signal detection through correlation detectionrequires the time corresponding to one known sequence constituting thepreamble PRB, the predetermined period is 80% of the time correspondingto one known sequence. Further, for example, when signal detectionthrough correlation detection requires the time corresponding to threeknown sequences constituting the preamble PRB, the predetermined periodis 2.5 times the time corresponding to one known sequence.

When the second determination signal is input in the period during whichthe gate signal is output, that is, the gate period described above, thegate unit 204 outputs, to the packet detection unit 109, a powerdetection signal including a power detection result indicating that thereception SNR, that is, the reception intensity of the signaltransmitted from the device with which the receiving device 100communicates is strong (corresponding to “CASE OF (c)” in FIG. 7).

In FIG. 6B, for (a) which indicates a power value when a signalreception intensity is weak, the first determination signal is output ata time point t1 at which the computed power value of the signal exceedsthe first power threshold value. However, the computed power value ofthe signal may not exceed the first power threshold value depending onthe signal reception intensity (not illustrated in FIG. 7).

For (b) which indicates a power value when a signal reception intensityis medium, the first determination signal is output at the time point t1at which the computed power value of the signal exceeds the first powerthreshold value, and the computed power value of the signal exceeds thesecond power threshold value at a time point t2′. Because the timebefore the time point t2′ exceeds the time from the time point tgs tothe time point tge during which the gate signal is output, the seconddetermination signal is not output (corresponding to “CASE OF (b)” inFIG. 7).

For (c) which indicates a power value when a signal reception intensityis strong, the first determination signal is output at the time point t1at which the computed power value of the signal exceeds the first powerthreshold value, and the computed power value of the signal exceeds thesecond power threshold value at a time point t2. Because the time pointt2 does not exceed the time from the time point tgs to the time pointtge during which the gate signal is output, the second determinationsignal is output (corresponding to “CASE OF (c)” in FIG. 7).

Although a timing at which the first determination signal is outputchanges slightly in response to a signal reception intensity, the powervalues indicated in (a) to (c), in which signal reception intensitiesare different, exceed the first power threshold value at the same timepoint for simplicity of description.

In FIG. 7, when a signal reception intensity is weak ((a) whichindicates a power value when a signal reception intensity is weak inFIG. 6B), the computed power value of the signal does not exceed thesecond power threshold value, and therefore the second determinationsignal is not output and the power detection signal is not generated(not illustrated in FIG. 7).

When a signal reception intensity is medium (see “CASE OF (b)” in FIG.7), the timing at which the computed power value of the signal exceedsthe second power threshold value is not in the period from the timepoint t1 (=time point tgs), at which the computed power value of thesignal exceeds the first power threshold value, to the time point tge,and therefore the power detection signal is not generated.

On the other hand, when a signal reception intensity is strong (see“CASE OF (c)” in FIG. 7), the timing at which the computed power valueof the signal exceeds the second power threshold value is in the periodfrom the time point t1 (=time point tgs), at which the computed powervalue of the signal exceeds the first power threshold value, to the timepoint tge, and therefore the power detection signal is generated.

Thus, when the reception intensity of the signal received by thereceiving device 100 is strong, the power detection unit 108 can output,to the packet detection unit 109, a power detection signal including apower detection result indicating that the reception intensity of thesignal transmitted from the device with which the receiving device 100communicates is strong. When the signal reception intensity is notstrong (medium or weak), a power detection signal is not output to thepacket detection unit 109.

When a power value exceeds the second power threshold value and thenfalls below the second power threshold value within the gate period, apower detection signal is generated, but the time for making a search ina wide gain range (see Tables 1 and 2) is secured, and thereforereception is possible.

The operation of power detection in the power detection unit 108 of thereceiving device 100 of the present embodiment will next be describedwith reference to FIG. 8. FIG. 8 is a flowchart illustrating an exampleof an operating procedure for power detection in the power detectionunit 108 of the receiving device 100 of the present embodiment.

In FIG. 8, the power detection unit 108 uses the power value firstdetermination unit 201 to determine whether the computed power valuecomputed by the power computation unit 107 exceeds the predeterminedfirst power threshold value (S1). When the power detection unit 108determines that the computed power value computed by the powercomputation unit 107 exceeds the predetermined first power thresholdvalue (YES at S1), the power detection unit 108 uses the gate signalgeneration unit 203 to output a gate signal for the predetermine period(time from the time point tgs to the time point tge) (S2).

While the gate signal generation unit 203 outputs the gate signal (YESat S3), when the power detection unit 108 determines that the computedpower value computed by the power computation unit 107 exceeds thepredetermined second power threshold value (YES at S4), the powerdetection unit 108 outputs, to the packet detection unit 109, a powerdetection signal including a power detection result indicating that thereception intensity of the signal transmitted from the device with whichthe receiving device 100 communicates is strong (S5).

(Gain Search Range Setting in the Gain Search Range Setting Unit 111 ofthe Receiving Device 100)

The detailed operation of gain search range setting in the gain searchrange setting unit 111 of the receiving device 100 of the presentembodiment will next be described with reference to FIG. 9. FIG. 9 is aflowchart illustrating an example of an operating procedure for gainsearch range setting in the gain search range setting unit 111 of thereceiving device 100 of the present embodiment.

In FIG. 9, the gain search range setting unit 111 obtains a receptionintensity estimation result output from the packet detection unit 109(S11). The gain search range setting unit 111 determines whether thereception intensity indicated in the reception intensity estimationresult output from the packet detection unit 109 is strong (S12).

When the gain search range setting unit 111 determines that thereception intensity indicated in the reception intensity estimationresult output from the packet detection unit 109 is strong (YES at S12),the gain search range setting unit 111 widens a gain search range forAGC processing (S13). For example, the gain search range setting unit111 widens the gain search range by adjusting a control range of a totalgain in the gain decision unit 112 to be the maximum range. The maximumrange of the control range of a total gain G is, for example, a range of[Gmin, Gmax], where Gmin is the minimum value of a total gain that isthe sum of a gain for the low noise amplifier 101 and a gain for thevariable gain amplifier 103, and Gmax is the maximum value of the totalgain.

That is, when the power value of the received signal is large enough toexceed the second power threshold value, the reception SNR of thereceived signal is large and the power rises quickly. Therefore, thetiming at which the signal is detected through power detection isearlier than the timing at which the signal is detected throughcorrelation detection.

Therefore, when the timing at which the signal is detected through powerdetection is earlier than the timing at which the signal is detectedthrough correlation detection, the gain search range setting unit 111can estimate that the reception intensity of the signal received by thereceiving device 100 is strong. Because it is necessary to significantlydecrease the total gain from the current setting, the gain search rangesetting unit 111 widens the gain search range of the total gain for AGCprocessing.

On the other hand, when the gain search range setting unit 111determines that the reception intensity indicated in the receptionintensity estimation result output from the packet detection unit 109 isnot strong (NO at S12), the gain search range setting unit 111 narrowsthe gain search range for AGC processing such that the gain search rangebecomes a range in which the total gain value is increased (S14). Forexample, the range in which the total gain value is increased is a rangeof [Rn×Gmax, Gmax], where Rn is a restriction rate of the control rangeof the total gain (for example, a value of about 0.3).

That is, when the power value of the received signal does not exceed thefirst power threshold value or the second power threshold value, thereception SNR of the received signal is small. It may be considered thatthe signal is detected, not through power detection but throughcorrelation detection.

Therefore, the gain search range setting unit 111 can estimate that thereception intensity of the signal received by the receiving device 100is not strong (medium or weak). Because it is not necessary tosignificantly decrease the total gain from the current setting, the gainsearch range setting unit 111 narrows the gain search range of the totalgain for AGC processing.

Accordingly, the convergence time of the AGC processing in the gaindecision unit 112 is short, and further, the gain decision unit 112 canreduce the convergence time of the AGC processing even though the timeof signal detection through correlation detection corresponding to thepredetermined preamble PRB is long. That is, it is possible to suppressa delay in the start of demodulation in the demodulation unit 113.

As described above, the receiving device 100 can determine whether thesignal is detected through power detection or through correlationdetection in the packet detection unit 109, and can set the gain searchrange of the total gain for AGC processing in accordance with the signaldetection method by which the signal is detected first.

The power detection unit of the receiving device 100 of the presentembodiment is not limited to the configuration of the power detectionunit 108 illustrated in FIG. 5. Variations of the power detection unitwill now be described with reference to the drawings.

(Detailed Configuration and Operation of a Power Detection Unit 108 a ofa First Variation)

The detailed configuration and operation of a power detection unit 108 aof a first variation will be described with reference to FIGS. 10A and10B. FIG. 10A is a block diagram illustrating in detail an internalconfiguration of the power detection unit 108 a of the first variation.FIG. 10B illustrates an example of a relationship of counting unitoutputs when signal reception intensities are strong and medium.

The power detection unit 108 a illustrated in FIG. 10A has a power valuedetermination unit 301, a counting unit 302, a count value firstdetermination unit 303, a count value second determination unit 304, thegate signal generation unit 203, and the gate unit 204. In thedescriptions of the units of the power detection unit 108 a illustratedin FIG. 10A, the descriptions about the same details as the units of thepower detection unit 108 illustrated in FIG. 5 are omitted orsimplified, and different details are described.

The power value determination unit 301 makes a comparison between thecomputed power value of the signal computed by the power computationunit 107 and a predetermined power determination threshold value, andoutputs a result of the comparison between the computed power value ofthe signal and the power determination threshold value to the countingunit 302. The power determination threshold value is, for example, apredetermined percentage of a signal power value for maximizing anoutput amplitude of the analog-digital conversion unit 104, and thispercentage is larger than the standby power target value (for example,50%).

Based on the output from the power value determination unit 301, thecounting unit 302 counts states in which the computed power value of thesignal computed by the power computation unit 107 exceeds the powerdetermination threshold value. That is, the counting unit 302 incrementsthe count value by 1 at predetermined intervals while the signal exceedsthe threshold value. Then, the counting unit 302 outputs the result(count value) to the count value first determination unit 303 and thecount value second determination unit 304.

When the computed power value of the signal computed by the powercomputation unit 107 is less than a specific value continuously for apredetermined period, the counting unit 302 resets the count value to 0(zero). When the reception intensity of the signal received by thereceiving device 100 is medium, the computed power value may or may notexceed the second power threshold value illustrated in FIG. 6B, andtherefore the count frequency of the count value in the counting unit302 is lowered.

The count value first determination unit 303 makes a comparison betweenthe count value output from the counting unit 302 and a predeterminedfirst count threshold value. When the count value output from thecounting unit 302 exceeds the first count threshold value, the countvalue first determination unit 303 outputs a first determination signalto the gate signal generation unit 203. The first count threshold valueis a predetermined value corresponding to the first power thresholdvalue used by the power value first determination unit 201.

The count value second determination unit 304 makes a comparison betweenthe count value output from the counting unit 302 and a predeterminedsecond count threshold value. When the count value output from thecounting unit 302 exceeds the second count threshold value, the countvalue second determination unit 304 outputs a second determinationsignal to the gate signal generation unit 203. The second countthreshold value is a predetermined value corresponding to the secondpower threshold value used by the power value second determination unit202.

In FIG. 10B, for (a) which indicates a power value when a signalreception intensity is weak, because the power value is less than thepower determination threshold value in the power value determinationunit 301, the first determination signal and the second determinationsignal are not output. Therefore, the power value is not illustrated inFIG. 10B, and the description of the power value is omitted.

For (b) which indicates a power value when a signal reception intensityis medium, the first determination signal is output at a time point t1′at which the count value corresponding to the computed power value ofthe signal exceeds the first count threshold value, and the count valuecorresponding to the computed power value of the signal exceeds thesecond count threshold value at the time point t2′. Because the timepoint t2′ exceeds the time from the time point tgs to the time point tgeduring which the gate signal is output as illustrated in FIG. 7, thesecond determination signal is not output.

For (c) which indicates a power value when a signal reception intensityis strong, the first determination signal is output at the time point t1at which the count value corresponding to the computed power value ofthe signal exceeds the first count threshold value, and the count valuecorresponding to the computed power value of the signal exceeds thesecond count threshold value at the time point t2. Because the timepoint t2 does not exceed the time from the time point tgs to the timepoint tge during which the gate signal is output as illustrated in FIG.7, the second determination signal is output.

Accordingly, even with the use of the configuration of the powerdetection unit 108 a illustrated in FIG. 10A, as in the power detectionunit 108 illustrated in FIG. 5, when the reception intensity of thesignal received by the receiving device 100 is strong, the powerdetection unit 108 a can output, to the packet detection unit 109, apower detection signal including a power detection result indicatingthat the reception intensity of the signal transmitted from the devicewith which the receiving device 100 communicates is strong. When thesignal reception intensity is not strong (medium or weak), a powerdetection signal is not output to the packet detection unit 109.

(Detailed Configuration and Operation of a Power Detection Unit 108 b ofa Second Variation)

The detailed configuration and operation of a power detection unit 108 bof a second variation will be described with reference to FIG. 11. FIG.11 is a block diagram illustrating in detail an internal configurationof the power detection unit 108 b of the second variation.

The power detection unit 108 b illustrated in FIG. 11 has the powervalue determination unit 301, the counting unit 302, a delay unit 401, asubtraction unit 402, and a number-of-times determination unit 403. Inthe descriptions of the units of the power detection unit 108 billustrated in FIG. 11, the descriptions about the same details as theunits of the power detection unit 108 a illustrated in FIG. 10A areomitted or simplified, and different details are described.

Based on the output from the power value determination unit 301, thecounting unit 302 counts states in which the computed power value of thesignal computed by the power computation unit 107 exceeds the powerdetermination threshold value. That is, the counting unit 302 incrementsthe count value by 1 at predetermined intervals while the signal exceedsthe threshold value. Then, the counting unit 302 outputs the result(count value) to the delay unit 401 and the subtraction unit 402. Thatis, as in FIG. 10B, the counting unit outputs increase with respect toan increase in time.

In the configuration with the count value first determination unit 303,the count value second determination unit 304, the gate signalgeneration unit 203, and the gate unit 204, the power detection unit 108a illustrated in FIG. 10A provides an equivalent for a determination ofwhether the reception intensity of the signal received by the receivingdevice 100 is strong, in response to an increment of the output (countvalue) from the counting unit 302 in a predetermined period, that is, aninclination with respect to time.

In contrast to this, the power detection unit 108 b illustrated in FIG.11 uses the delay unit 401 to delay the output (count value) from thecounting unit 302 for a predetermined period. The delay unit 401 delaysthe output (count value) from the counting unit 302 for thepredetermined period, and outputs the value to the subtraction unit 402.

The description will be given with reference to FIG. 10B. When a delayin the predetermined period is t2−t1, the value input from the countingunit 302 to the subtraction unit 402 is the count at the time point t2,and the value input from the delay unit 401 to the subtraction unit 402is the count value at the time point t1.

The subtraction unit 402 performs a subtraction between the output(count value) from the counting unit 302 and the output (count value)from the counting unit 302 that is delayed by the delay unit 401, andoutputs a subtraction result to the number-of-times determination unit403. Accordingly, the subtraction unit 402 can obtain an increment ofthe output (count value) from the counting unit 302 in the predeterminedtime. That is, when a delay in the predetermined period is t2−t1, theincrement is a value obtained by subtracting the count value at the timepoint t1 from the count at the time point t2.

The number-of-times determination unit 403 makes a comparison betweenthe output from the subtraction unit 402 and a predeterminednumber-of-times threshold value. When the output from the subtractionunit 402 exceeds the number-of-times threshold value, thenumber-of-times determination unit 403 outputs, to the packet detectionunit 109, a power detection signal including a power detection resultindicating that the reception intensity of the signal transmitted fromthe device with which the receiving device 100 communicates is strong.

Accordingly, even with the use of the configuration of the powerdetection unit 108 b illustrated in FIG. 11, as in the power detectionunit 108 illustrated in FIG. 5, when the reception intensity of thesignal received by the receiving device 100 is strong, the powerdetection unit 108 b can output, to the packet detection unit 109, apower detection signal including a power detection result indicatingthat the reception intensity of the signal transmitted from the devicewith which the receiving device 100 communicates is strong. When thesignal reception intensity is not strong (medium or weak), a powerdetection signal is not output to the packet detection unit 109.

(Detailed Configuration and Operation of a Power Detection Unit 108 c ofa Third Variation)

The detailed configuration and operation of a power detection unit 108 cof a third variation will be described with reference to FIGS. 12A and12B. FIG. 12A is a block diagram illustrating in detail an internalconfiguration of the power detection unit 108 c of the third variation.FIG. 12B illustrates an example of a relationship of integration unitoutputs when signal reception intensities are strong and medium.

The power detection unit 108 c illustrated in FIG. 12A has a power valuedetermination unit 501, a power integration unit 502, an integrationvalue first determination unit 503, an integration value seconddetermination unit 504, the gate signal generation unit 203, and thegate unit 204. In the descriptions of the units of the power detectionunit 108 c illustrated in FIG. 12A, the descriptions about the samedetails as the units of the power detection unit 108 illustrated in FIG.5 are omitted or simplified, and different details are described.

The power value determination unit 501 makes a comparison between thecomputed power value of the signal computed by the power computationunit 107 and a predetermined power integration threshold value. When thecomputed power value of the signal exceeds the power integrationthreshold value, the power value determination unit 501 outputs anintegration start signal to the power integration unit 502. The powerintegration threshold value is, for example, a predetermined percentageof a signal power value for maximizing an output amplitude of theanalog-digital conversion unit 104, and this percentage is larger thanthe standby power target value (for example, 50%).

Based on the integration start signal output from the power valuedetermination unit 501, the power integration unit 502 starts timeintegration of the computed power value of the signal computed by thepower computation unit 107. When the reception intensity of the signalreceived by the receiving device 100 is strong, a power integrationvalue increases more quickly than when the reception intensity of thesignal is medium. The power integration unit 502 outputs an integrationvalue of the computed power value of the signal computed by the powercomputation unit 107 to the integration value first determination unit503 and the integration value second determination unit 504.

The integration value first determination unit 503 makes a comparisonbetween the integration value output from the power integration unit 502and a predetermined first integration threshold value. When theintegration value output from the power integration unit 502 exceeds thefirst integration threshold value, the integration value firstdetermination unit 503 outputs a first determination signal to the gatesignal generation unit 203. The first integration threshold value is apredetermined value corresponding to the first power threshold valueused by the power value first determination unit 201.

The integration value second determination unit 504 makes a comparisonbetween the integration value output from the power integration unit 502and a predetermined second integration threshold value. When theintegration value output from the power integration unit 502 exceeds thesecond integration threshold value, the integration value seconddetermination unit 504 outputs a second determination signal to the gatesignal generation unit 203. The second integration threshold value is apredetermined value corresponding to the second power threshold valueused by the power value second determination unit 202.

In FIG. 12B, for (a) which indicates a power value when a signalreception intensity is weak (not illustrated), because the power valueis less than the power determination threshold value in the power valuedetermination unit 501, the first determination signal and the seconddetermination signal are not output, and the description of the powervalue is omitted.

For (b) which indicates a power value when a signal reception intensityis medium, the first determination signal is output at the time pointt1′ at which the integration value corresponding to the computed powervalue of the signal exceeds the first integration threshold value, andthe integration value corresponding to the computed power value of thesignal exceeds the second integration threshold value at the time pointt2′. Because the time point t2′ exceeds the time from the time point tgsto the time point tge during which the gate signal is output, the seconddetermination signal is not output.

For (c) which indicates a power value when a signal reception intensityis strong, the first determination signal is output at the time point t1at which the integration value corresponding to the computed power valueof the signal exceeds the first integration threshold value, and theintegration value corresponding to the computed power value of thesignal exceeds the second integration threshold value at the time pointt2. Because the time point t2 does not exceed the time from the timepoint tgs to the time point tge during which the gate signal is output,the second determination signal is output.

Accordingly, even with the use of the configuration of the powerdetection unit 108 c illustrated in FIG. 12A, as in the power detectionunit 108 illustrated in FIG. 5, when the reception intensity of thesignal received by the receiving device 100 is strong, the powerdetection unit 108 c can output, to the packet detection unit 109, apower detection signal including a power detection result indicatingthat the reception intensity of the signal transmitted from the devicewith which the receiving device 100 communicates is strong. When thesignal reception intensity is not strong (medium or weak), a powerdetection signal is not output to the packet detection unit 109.

Although various embodiments have been described above with reference tothe drawings, it is obvious that the present disclosure is not limitedto such examples. It is apparent that those skilled in the art would beable to conceive various examples of changes or modifications within thescope indicated in the claims, and it should be appreciated that theseexamples are also included in the technical scope of the presentdisclosure.

The present disclosure has been described above with an example in whichthe receiving device 100 is configured with, for example, hardwareresources. However, part of the receiving device 100 may be configuredwith software that collaborates with the hardware resources.

The units (components) of the receiving device 100 of the presentembodiment described above are typically implemented as large scaleintegration (LSI) chips, which are integrated circuits. An eachindividual component may be contained on a single LSI chip, or some orall components may be contained on a single LSI chip. The integratedcircuit technique is LSI here, but may be referred to as integratedcircuit (IC), system LSI, super LSI, or ultra LSI depending on adifference in a degree of integration.

The integrated circuit technique is not limited to LSI, and thecomponents may be implemented using dedicated circuits orgeneral-purpose processors. After the manufacture of LSI chips, fieldprogrammable gate arrays (FPGAs), or reconfigurable processors withwhich the connection and setting of circuit cells inside the LSI chipsare reconfigurable may be used.

In addition, if an integrated circuit technology that replaces LSIemerges with the advance of the semiconductor technology or with theadvent of another derivative technology, the units of the receivingdevice 100 may be integrated using that technology. There is apossibility of, for example, applying the biotechnology.

The present disclosure is useful as a receiving device that enhances thespeed of convergence of AGC and suppresses degradation of the detectionaccuracy for a received signal, regardless of whether a device withwhich the receiving device communicates is changed or moved.

What is claimed is:
 1. A receiving device receiving a signal in areceiving antenna comprising: a gain controller that adjusts a gain inthe receiving device in response to information about power of thesignal; and a signal detector that determines whether, within apredetermined period after the information related to the power of thesignal exceeds a first threshold value, the information related to thepower of the signal exceeds a second threshold value which is largerthan the first threshold value, wherein the gain controller adjusts asearch range of the gain in the receiving device based on adetermination result of the signal detector with respect to theinformation related to the power of the signal.
 2. The receiving deviceaccording to claim 1, wherein the signal detector includes a powerdetector that determines detection of the signal based on theinformation related to the power of the signal; and a correlationdetector that determines detection of the signal based on a correlationbetween the signal and a known sequence.
 3. The receiving deviceaccording to claim 1, wherein the gain controller widens the searchrange of the gain, in a case where the determination result of thesignal detector is that the information related to the power of thesignal exceeds the first threshold value and the information related tothe power of the signal exceeds the second threshold value within thepredetermined period.
 4. The receiving device according to claim 1,wherein the gain controller narrows the search range of the gain, in acase where the determination result of the signal detector is that theinformation related to the power of the signal exceeds the firstthreshold value and the information related to the power of the signaldoes not exceed the second threshold value within the predeterminedperiod, or in a case where the determination result of the signaldetector is that the information related to the power of the signal doesnot exceed the first threshold value.
 5. The receiving device accordingto claim 2, wherein the power detector further includes a first powervalue determinator that outputs a first determination signal in a casewhere the information related to the power of the signal exceeds thefirst threshold value; a second power value determinator that outputs asecond determination signal in a case where the information related tothe power of the signal exceeds the second threshold value; a first gatesignal generator that outputs a predetermined gate signal for thepredetermined period from an output timing of the first determinationsignal; and a first gate that outputs a power detection signalindicating a strong electric field in a case where the seconddetermination signal is output in the predetermined period.
 6. Thereceiving device according to claim 1, wherein the information relatedto the power of the signal is a count value obtained by counting thenumber of times the power of the signal exceeds a third threshold value.7. The receiving device according to claim 1, wherein the informationrelated to the power of the signal is an integration value of the powerof the signal.
 8. The receiving device according to claim 6, wherein thepower detection unit further includes a first counter that indicates thecount value; a first count value determinator that outputs a firstdetermination signal in a case where the count value exceeds the firstthreshold value; a second count value determinator that outputs a seconddetermination signal in a case where the count value exceeds the secondthreshold value; a second gate signal generator that outputs apredetermined gate signal for the predetermined period from an outputtiming of the first determination signal; and a second gate that outputsa power detection signal indicating a strong electric field in a casewhere the second determination signal is output in the predeterminedperiod.
 9. The receiving device according to claim 7, wherein the powerdetector further includes a first integration value determinator thatoutputs a first determination signal in a case where an integrationvalue of the power of the signal exceeds the first threshold value; asecond integration value determinator that outputs a seconddetermination signal in a case where the integration value of the powerof the signal exceeds the second threshold value; a third gate signalgenerator that outputs a predetermined gate signal for the predeterminedperiod from an output timing of the first determination signal; and athird gate that outputs a power detection signal indicating a strongelectric field in a case where the second determination signal is outputin the predetermined period.